The studies are aimed at providing information on the anatomical brain distribution of steroid hormone target cells and to interrelate these target cells to aminergic and peptidergic neuronal systems. Thaw-mount autoradiography alone or combinations of autoradiography with immunohistochemistry or fluorescence microscopy will be applied. The steroid hormones used include radioactively labeled estrogens, androgens, progestins and adrenal corticoids. Hypothalamic and extrahypothalamic limbic structures will be studied in different vertebrate species. Ontogenetic studies will seek to obtain information on the appearance of estrogen, androgen and adrenal steroid receptors during fetal development. The influence of hormonal treatment on the modulation of hormone receptors will be studied by quantitative autoradiography in order to obtain information on selective responses of individual brain nuclei and the relationships to the aminergic and peptidergic systems. The results are expected to aid in the understanding of interactions between steroid hormones with the central nervous system as relevant for the regulation of neuroendocrine events, behavior, autonomic and mental processes in health and disease.